Electrical supply system for low current loads

ABSTRACT

An electrical supply system (10) for use with low current loads (12) disposed in hazardous areas, is described. Electricity is supplied to the low current load (12) from a local source (46) in response to mechanical energy from a fluid medium supplied from a remote pressure source (24).

The present invention relates to an electrical supply system for lowcurrent loads and particularly, but not exclusively to such anelectrical supply system for use with low current loads disposed inhazardous areas.

When an electrical supply system is disposed in a hazardous area, thereis always numerous cables, junction-boxes and glands and the likedisposed within the hazardous area. During failure of such electricalequipment, for example during an emergency, each of these cables,junction-boxes and glands are susceptible to primary and/or secondarymeans of sparking. Such sparking can be particularly dangerous inhazardous areas and therefore conventional electrical supply means canprovide a relatively high potential risk to the user.

It is desirable that electrical equipment used in a hazardous areashould be disposed within a flameproof enclosure. Such an enclosureshould be able to withstand, without damaging the equipment, anexplosion of flammable gas or vapour. Such explosions may occur inhazardous areas and it is desirable that the equipment should operate toits usual rating in such conditions. The flameproof enclosure shouldalso prevent the transmission of flame such as would ignite flammablegases or vapours in the surrounding atmosphere. It is also desirablethat the flameproof enclosure should be ventilated by a purging streamof dry air or inert gas to provide a plenum of safe atmosphere.

It is an object of the present invention to provide an electrical supplysystem which obviates or mitigates at least one of the aforementionedproblems.

This is achieved by providing an electrical supply system (a.c. or d.c.)from a local source in response to mechanical energy from a fluid mediumsupplied from a remote pressure source.

In one embodiment electrical energy for fluorescent lighting is providedby an alternator, the rotor of which is coupled to and driven by animpeller. Compressed air from a remote source is fed to the blades ofthe impeller causing the impeller to rotate and provide kinetic energyto the rotor. Several lights are connected in parallel.

According to a first aspect of the present invention there is providedan electrical supply system for supplying electricity to a low currentload, said electrical supply system comprising compressor means forgenerating pressure in a fluid medium a housing coupled to saidcompressor means by flow and return conduits, said housing containingenergy conversion means for converting energy of said fluid medium toelectricity, said energy conversion means including a rotatable impellerfor receiving said fluid medium and for converting energy in said fluidmedium into rotational energy, first magnet means coupled to saidimpeller, second magnet means spaced apart from said first magnet means,said first and said second magnet means being spaced apart along, androtatable about, a common axis of rotation, said first and second magnetmeans forming a magnetic coupling whereby said rotational energy of saidimpeller is transferred to said second magnet means, and an alternatorcoupled to said second magnet means for converting the rotational energyof said second magnet means into electrical energy for supply to saidlow current load.

Conveniently said fluid means is compressed air.

Alternatively said fluid medium is a compressed or pressurised gas.Alternatively also said fluid medium is a compressed or pressurisedliquid.

Preferably said compressor means is located remotely from said lowcurrent load. Conveniently said conduits provide a path through whichsaid medium is supplied to the blades of said impeller and a paththrough which said medium is returned to said compressor.

Preferably at least one fluid medium control element is mounted on eachof the flow and return conduits. Conveniently said conduits are made ofstainless steel or plastic.

Preferably said low current load is a light source. Conveniently saidlight source is a fluorescent light tube. Preferably also a plurality ofsaid low current loads are connected in parallel.

According to a second aspect of the present invention there is providedan energy conversion device for providing electrical energy for a lowcurrent load, said energy conversion device comprising impeller meansfor receiving a fluid medium and for converting energy in said fluidmedium into rotational energy, said fluid medium being supplied from aremote fluid medium source, first magnet means coupled to said impellermeans, second magnet means spaced apart from said first magnet means,said first and said second magnet means being spaced apart along, androtatable about, a common axis of rotation, said first and said secondmagnet means forming a magnetic coupling whereby said rotational energyof said impeller means is transferred to said second magnet means, andalternator means coupled to said second magnet means for converting saidrotational energy of said second magnet means into electrical energy.

Preferably said impeller means is an impeller with a plurality of bladesand, in use, said fluid medium is incident on the blades of saidimpeller to cause rotational movement of said impeller.

Conveniently said fluid medium is compressed air.

Alternatively said fluid medium is a compressed or pressurised gas orliquid.

Preferably a plurality of said low current loads are connected inparallel Conveniently said low current load is a light source.

According to a third aspect of the present invention combination withthe accompanying drawings in which:

FIG. 1 is a diagrammatic view of an electrical supply system inaccordance with the present invention;

FIG. 2 is a front elevational view of a lighting unit for use in thesystem shown in FIG. 1;

FIG. 3 is a plan view of the lighting unit shown in FIG. 2;

FIG. 4 is a plan view of the top of the lighting unit shown in FIG. 2;

FIG. 5 is a plan view of the bottom of the lighting unit shown in FIG.2;

FIG. 6 is a sectional view, drawn to a larger scale, of part of thelighting unit shown in FIGS. 2 to 5, and

FIGS. 7 to 12 are cross-sectional views of FIG. 6 taken on lines 7--7 to12--12 respectively, and

FIGS. 13a-13c are diagrammatic views of three alternative arrangementsof the electrical supply system shown in FIGS. 1 to 12.

Reference is firstly made to FIG. 1 of the drawings, which shows anelectrical supply system generally indicated by reference numeral 10.The supply system 10 provides an electrical supply for low current loadssuch as fluorescent strip lighting disposed in a hazardous area 11. Thesupply system 10 comprises identical lighting units 12, 12a and 12bconnected in parallel. The lighting units 12, 12a and 12b are operatedfrom a remote location 14 outwith the hazardous area 11 as will bedescribed. Compressed air, supplied from the remote location 14 to thelighting units 12, 12a and 12b causes these lighting units to beenergised to supply light as will also be described.

The compressed air is supplied from a compressed air supply and controlsystem 14 located remotely to the lighting units 12, 12a and 12b along afirst stainless steel pipe 16. When the compressed air is received bythe lighting units 12, 12a and 12b the compressed air drives a generatordisposed within each unit 12, 12a and 12b and the air eventually expandsand returns to the remote compressor 24 along second stainless steelpipe 18. Water traps 20, 20a and 20b are located adjacent lighting unit12, 12a and 12b respectively to trap water contained in the compressedair. In particular the compressed air from compressor 24, which canattain pressures up to 1000 p.s.i., passes through drier 26 beforeentering an air receiver 27 and a series of pressure regulationelements.

The air receiver 27 output passes through a first pressure regulator 28,an oil trap 30, pressure gauge 32 and a water trap 34 before reaching apressure regulator control panel 35. The oil trap 30 and water trap 34ensure that the compressed air supplied to pipe 16 is relatively clean.The pressure gauge 32 provides an indication of the pressure of thecompressed air in the system. Pressure regulator control panel 35 allowscontrol of the pressure valve of the compressed air supplied to pipe 16.The compressed air supplied to pipe 16 passes through a second regulator36 before entering pipe 16. The pressure gauge 32 is connected to analarm system (not shown) and the flow of compressed air may be shut downin an over-pressure situation by closing regulators inside controlpanels 22 and 35. Similarly if pressure gauge 32 gives an indication ofunder-pressure in the system, regulators inside 22 and 35 are alsoclosed. The pressure of compressed air supplied to pipe 16 must besufficient to allow lighting units 12, 12a and 12b to be driven in amanner as will be described. The air returned along pipe 18 passesthrough pressure drop control panel 22 which provides control of thepressure of expanded air entering compressor 24. The air is againcompressed and treated and then passed to the lighting units 12 asdescribed above.

Similar lighting systems designated 11a, 11b can be operated in parallelwith 11 from the remote compressed air supply and control system 14. Thenumber of lighting units which may be used is determined by the outputpressure of the compressor 24 and the pressure capabilities of thepipes.

Reference is now made to FIGS. 2 to 5 of the drawings which are variousviews of the lighting unit 12 shown in FIG. 1. The lighting unit 12comprises two fluorescent lighting tubes 40a and 40b mounted on castiron brackets 42a and 42b which permit the unit 12 to be suspended froma ceiling. The brackets 42a and 42b are constructed to substantiallywithstand any vibrations created by the force of the compressed airdriven system and by explosions in the hazardous area. Tubes 40a and 40bhave electrical connections 44a and 44b respectively which allow thefluorescent tubes to be energised by electrical signals emitted from apneumatic--electric conversion unit 46 mounted above the tubes 40a, 40b.Each lighting tube 40a, 40b has a rating of 60 Watts. When operated froma generator providing a 110 volt output, each tube 40a, 40b requiresapproximately 0.5 amps of current. As best seen in FIG. 2, unit 46 twoexternal connections either of which can be connected to supply pipe 16or return pipe 18. The compressed air can enter unit 46 through pipeconnection 46 and leave through pipe connection 48, or can enter throughpipe connection 48 and leave through pipe connection 46. However, forthe purpose of explanation the diagrams show one direction of flow only.Pipe connection 46 is designated as an inlet pipe connection and iscoupled to inlet pipe 16 and pipe connection 48 is designated as anoutlet connection and is coupled to outlet pipe 18. When compressed airfrom pipe 16 enters unit 46 via inlet 48, the compressed air rotates agenerator which generates electricity, as will be described in detail.

Reference is now made to FIG. 2 and FIGS. 6 to 12 of the drawings, FIG.6 being an elevational view of part of the unit 46 drawn to a largerscale, and FIGS. 7 to 12 being various cross-sectional views taken onlines 7--7 to 12--12 of FIG. 6. The pneumatic-electrical conversion unit46 contains within its housing an air pressure to rotary motionconvertor, generally indicated by numeral 52 (FIG. 6), and a rotarymotion to electrical energy convertor in the form of a single-phasebrushless alternator, generally indicated by 54. The air pressure torotary motion convertor 52 receives compressed air through inlet 48, thecompressed air passes into a chamber 60 and is incident on the blades 56of an impeller 58, best seen in FIG. 8, disposed in the chamber 60. Thecompressed air acts on the blades 56 of impeller 58, to rotate theimpeller in the direction of arrow 61. This causes a correspondingrotation of a first shaft 62. The rotation of the impeller 58 providesconstant output torque for shaft 62. The compressed air exits chamber 60via channels 64 and exit holes 66 disposed around the circumference ofcircular plate 69, as best seen in FIGS. 6 and 7. This air flows alongthe outside of the convertor 52 and alternator 54 along pipe 50 over thesurface of fluorescent tubes 40a, 40b above the screen 57 to help tocool the tubes and purge the system of existing surrounding atmospherebefore being returned via tube 18 to the remote pressure source.

The stream of air passing over tubes 40a, 40b and above screen 57provides the electrical elements within the unit 46 with a plenum oftreated atmosphere. A sufficient flow of air within the lighting unit 12provides a positive pressure which substantially removes any flammablegases within lighting unit 12. The positive pressure of the air flowalso prevents flammable gases from entering the lighting unit 12. In thecase of the failure of the pressurising air flow, a warning is given toallow suitable precautionary measures to be taken.

The first shaft 62 is coupled to a second co-axial shaft 68 via amagnetic coupling 70. Magnets 72a and 72b mounted on first and secondshafts 62 and 68 respectively, cause second shaft 68 to rotate withfirst shaft 62 without slip. The magnetic coupling 70 of first andsecond shafts 62 and 68 minimises mechanical losses in the system andreduces the likelihood of any particles of dust and moisture enteringgearing arrangement 76 and alternator 54.

Second shaft 68 is coupled to a third shaft 74 via a gearing arrangement76. The gearing arrangement 76 ensures that third shaft 74 is driven torotate an angular velocity sufficient to generate an adequate supply ofelectricity. The third shaft 74 is coupled to the rotor 78 of alternator54 via a magnetic coupling 80 similar to that hereinbefore described. Asthe third shaft 74 rotates, the rotor 78 of alternator rotates with thethird shaft 74 with minimal slip.

Permanent magnets 82 and 82b (best seen in FIG. 10) and stator coils84a, 84b, 84c and 84d (best seen in FIG. 12) are mounted within thehousing 85 of alternator 54. As rotor 78 rotates electrical signals aregenerated from the stator coils in a manner well known in the art. Therotor 78 is driven at such a speed and is constructed in such a manneras to induce acceptible exitation and output voltage to produce anuninterrupted power supply. The alternator incorporates voltage limitdevices and is provided with double insulation. The electricalconnections of the alternator 54 are not shown in the interest ofclarity. An electrical output terminal 86 is mounted on alternator 54.This terminal 86 is connected to terminals 44a and 44b of fluorescenttubes 40a and 40b. Thus electrical signals generated at terminal 86 dueto the rotation of rotor 78 cause fluorescent tubes 40a and 40b to beenergised.

Reference is now made to FIGS. 13a to 13c of the drawings which showthree alternative arrangements for the flow of compressed air throughthe unit 46 and through a certified appliance 88. It is understood thatthe certified appliance 88 is a low current load such as a lighting unitand that the electrical connections between unit 46 and appliance 88 areshown by dotted lines 90. Unit 46 provides a certified power supply forthe certified appliance 88.

In the arrangement shown in FIG. 13A, the flow of compressed air frominlet 16 to outlet 18 passes through the certified appliance both beforethe compressed air flows into unit 46 and after the compressed air exitsunit 46. As hereinbefore described, the inlet and outlet connections maybe reversed. In the arrangement shown in FIG. 13B, the compressed airflows through unit 46 before flowing through the certified appliance 88and in the arrangement shown in FIG. 13c the compressed air flowsthrough the appliance 88 before flowing through the unit 46.

Various modifications may be made to the embodiment hereinbeforedescribed without departing from the scope of the present invention. Anysuitable compressed fluid may be used instead of compressed air. Thebrackets and control box of the lighting unit may be made of stainlesssteel. One of the magnetic couplings in the convertor or alternator maybe replaced by a mechanical coupling.

Any low current load may be operated by the system, for example a clock.The alternator may be of the brush type if desired. The maximum loadeach pneumatic to electrical conversion unit can power is approxiately500 Watts, and the maximum output current of each pneumatic toelectrical conversion unit is approximately 5A. The permanent magnets ofthe alternator may be disposed in any suitable position for obtaining adesired electrical output and coils could be used in combination withthe magnets to provide sufficient excitation energy. In addition to thepurging of the system a separate, low pressure start line may be used topre-purge the system. The system can also be adapted to be used with anyapparatus or structure which is designed to be substantially "explosionproof".

Advantages associated with the present invention are that the electricalsupply system is suitable for use in hazardous environments, class 1,group 1 and which is also independant of the purging system. Theelectrical equipment is disposed within a flameproof and substantiallyexplosion proof enclosure. The probability of a dangerous gassurrounding a dangerous electrical condition is minimal. The system iscompletely independent and is constantly monitored and alarmed. As thereare no junction boxes, cables or glands the chances of sparking arealmost eliminated thus reducing the high potential risk of usingelectrical equipment in hazardous areas. In addition the system isalmost maintenance free in as much as there are no servicable parts.This ensures that the original specification and tolerances aremaintained.

I claim:
 1. An electrical supply system for supplying electricity to aplurality of low current loads, said electrical supply systemcomprising:a plurality of low current loads, a fluid medium, compressormeans for generating pressure in said fluid medium, flow and returnconduits, a plurality of housings associated with said plurality of lowcurrent loads and coupled to said compressor means by said flow andreturn conduits, said housings containing energy conversion means forconverting energy of said fluid medium to electricity, each said energyconversion means comprising a rotatable impeller for receiving saidfluid medium and for converting energy in said fluid medium intorotational energy, first magnet means coupled to said impeller, secondmagnet means spaced apart from said first magnet means, said first andsaid second magnet means being spaced apart along, and rotatable about,a common axis of rotation, said first and said second magnet meansforming a magnetic coupling whereby said rotational energy of saidimpeller is transferred to said second magnet means, and a generatorcoupled to said second magnet means for converting the rotational energyof said second magnet means into electrical energy for supply to saidplurality of low current loads.
 2. The electrical supply system of claim1, wherein the fluid medium comprises compressed air.
 3. The electricalsupply system of claim 1, wherein the fluid medium comprises acompressed or pressurized gas.
 4. The electrical supply system of claim1, wherein the fluid medium comprises a compressed or pressurizedliquid.
 5. The electrical supply system of claim 1, further comprising aplurality of low current loads and wherein the compressor means isremotely located with respect to the low current load.
 6. The electricalsupply system of claim 1, whereinthe conduits provide a path throughwhich the medium is supplied to the blades of the impeller and a paththrough which the medium is returned to the compressor.
 7. Theelectrical supply system of claim 1, whereinat least one fluid mediumcontrol element is mounted on each of the flow and return conduits. 8.The electrical supply system of claim 1, wherein the conduits are madeof stainless steel or plastic.
 9. The electrical supply system of claim1, further comprising a plurality of low current loads and wherein thelow current load comprises a light source.
 10. The electrical supplysystem of claim 9, wherein the light source comprises a fluorescentlight tube.
 11. The electrical supply system of claim 1 and furthercomprising a plurality of low current loads connected in parallel to oneanother.
 12. An energy conversion device for providing electrical energyfor a plurality of low current loads, said energy conversion devicecomprising:a plurality of low current loads, a fluid medium, a pluralityof housings associated with said plurality of low current loads saidhousings comprising a remote source of said fluid medium, impeller meansfor receiving said fluid medium and for converting energy in said fluidmedium into rotational energy, first magnet means coupled to saidimpeller means, second magnet means spaced apart from said first magnetmeans, said first and said second magnet means being spaced apart along,and rotatable about, a common axis of rotation, said first and saidsecond magnet means forming a magnetic coupling whereby said rotationalenergy of said impeller means is transferred to said second magnetmeans, and a generator means coupled to said second magnet means forconverting said rotational energy of said second magnet means intoelectrical energy for supply to said plurality of low current loads. 13.The energy conversion device of claim 12, wherein the fluid mediumcomprises compressed air.
 14. The energy conversion device of claim 12,wherein the fluid medium comprises a compressed or pressurized gas orliquid.
 15. The energy conversion device of claim 12 and furthercomprising a plurality of low current loads connected in parallel to oneanother.
 16. A method of supplying electrical energy to a plurality oflow current loads comprising the steps of:supplying a fluid medium froma remote fluid medium source to a plurality of housings associated witha plurality of low current loads said housings having an energyconversion device comprising an impeller and a generator coupledtogether by first and second magnet means spaced apart along, androtatable about, a common axis of rotation and forming a magneticcoupling, said having being disposed in close proximity to saidplurality of low currently loads; converting energy in said fluid mediuminto rotational energy by said impeller; coupling the rotational energyof said impeller to rotate the first magnet means about said common axisand magnetically coupling the second magnetic means to rotate about thesame axis whereby rotational energy is transferred from said impeller tosaid second magnet means and to said generator, and converting saidrotational energy of said generator into electrical energy for supply tosaid plurality of low current loads.